The paper describes the general proposal, function and performance of a prognostics system for fatigue crack growth in airframe structures. The prognostic is an important part of a superior Structural Health Monitoring System (SHM). An aim of the prognosis is estimation / prediction of a system / subsystem / structure remaining life, i.e. the time at which damage (crack, corrosion, wear, delamination, disbonding, etc.) will result in a failure of the considered element.It brings significant benefits in an aircraft service and maintenance. It shifts a structural maintenance program on an advanced level and brings significant benefits for an aircraft operator like efficient maintenance planning, effective aircraft usage, service cost decrease, safety increase,etc.